Traditional RADAR is leveraged by aircraft to identify terrain, weather hazard regions, and other environmental factors. Weather RADAR can detect the motion of large scattering particles such as rain, snow, or hail. These larger particles can provide the reflective ranges for determining regions of turbulence or wind shear. RADAR systems dependent upon these larger particles may be insensitive, or blind, to atmospheric phenomena containing small particles. For example, regions of clear air turbulence, building thunderstorms, or decaying thunderstorms are not detected by such RADAR systems.
Light detection and ranging (LIDAR) techniques may be used to measure properties of scattered light. However, traditional LIDAR systems are based upon coherent heterodyne LIDAR techniques. Coherent heterodyne LIDAR requires a reference laser referred to as the local oscillator (LO). In heterodyne systems, light from the LO is mixed with the signal returned from the scattering medium or atmosphere. A frequency of the resultant heterodyne signal is compared to the expected frequency which is the difference between the transmitter and the LO. The difference between the measured and expected frequency is the target Doppler shift which is proportional to the target velocity. Thus, the heterodyne solution must maintain and carefully control the frequency offset between the transmitter and LO in order to accurately calculate the target Doppler shift to determine the velocity.
Controlling this frequency offset is generally a challenge. For example, the transmitter laser frequency may be measured and controlled to compensate for LO laser drift, also the frequency offset between the transmitter and the LO may be measured and tracked for each measurement firing of the laser. Frequency offset control may often involve phase locked loop (PLL) electronics and various other complex techniques. In addition to the second laser source for generating an LO signal, frequency offset control techniques generally require complex, heavy, power-hungry, and expensive components to be deployed as part of the LIDAR system.